ISO/IEC 15909-2:2011 defines an XML-based transfer format for Petri nets, which are defined conceptually and mathematically in ISO/IEC 15909-1. This transfer format enables the exchange of Petri nets among different Petri net tools and among different parties. Moreover, ISO/IEC 15909-2:2011 defines some concepts and XML-based syntax for defining the detailed graphical appearance of Petri nets.The focus of ISO/IEC 15909-2:2011 is on the transfer format for Place/Transition Nets, High-level Petri Nets and Symmetric Nets. The presentation, however, is structured in such a way that it is open for future extensions, so that other versions of Petri nets can be added later. The exact definition of this extension mechanism, called Petri net type definition, is not defined in ISO/IEC 15909-2:2011; it will be defined in ISO/IEC 15909-3. The transfer format will be used to transfer specifications of systems developed in High-level Petri Nets between tools to facilitate the development of systems in teams. ISO/IEC 15909-2:2011 is written as a reference for developers of Petri net tools. It will also be useful for researchers who define new versions and variants of Petri nets.